1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, which are suitable for an image pickup optical system of an image pickup apparatus, such as a video camera, a silver-halide camera, a digital camera, a TV camera, or a monitoring camera.
2. Description of the Related Art
In recent years, a zoom lens used with an image pickup apparatus is required to have a high zoom ratio and a high resolution and to be compact. Further, when a vibration is applied to the zoom lens during photography of a subject, image blur occurs, and hence the zoom lens is required to have an image stabilization function for avoiding the image blur. There has hitherto been known a zoom lens having a four-unit configuration including, in order from an object side to an image side, first, second, third, and fourth lens units having positive, negative, positive, and positive refractive powers.
In Japanese Patent Application Laid-Open No. 2002-031756, there is disclosed a four-unit zoom lens in which a second lens unit and a third lens unit are moved to perform zooming, and a fourth lens unit is moved to correct an image plane movement accompanying the zooming. In Japanese Patent Application Laid-Open No. H11-311742, there is disclosed a four-unit zoom lens in which a second lens unit is moved to perform zooming, a fourth lens unit is moved to correct an image plane movement accompanying the zooming, and a third lens unit is moved in its entirety in a direction perpendicular to an optical axis to correct image blur. In Japanese Patent Application Laid-Open No. 2003-322795, there is disclosed a four-unit zoom lens in which second and fourth lens units are moved during zooming, and a lens portion forming a part of a third lens unit is moved in a direction perpendicular to the optical axis to correct image blur.
In the zoom lens having the image stabilization function, when an image stabilization lens unit has a large size and heavy weight, in order to cause the image stabilization lens unit to operate, a driving source having large driving power needs to be adopted. As a result, optical system units including the driving source are increased in size as a whole, and the zoom lens is increased in weight. Moreover, when the image stabilization lens unit is increased in weight, responsiveness of an image stabilization operation is reduced, with the result that fast control becomes difficult.
With a method in which, for image stabilization, lens units forming a part of the zoom lens are decentered in parallel in the direction perpendicular to the optical axis, the image stabilization lens unit is reduced in size and weight, and high-speed image stabilization is easy. However, large decentering aberration occurs during the image stabilization, and there is a tendency for an optical characteristic to be reduced significantly. Therefore, it is important for the zoom lens having an image stabilization mechanism to have the lens unit for image stabilization that is small in size and weight, and a small degradation in optical characteristic during the correction of the image blur (during the image stabilization).